Ok lets go into details a little more:

User <--> FS <--> Provider

When User sends a fax, provider detects tones and renegotiates with t38. I can handle this case fine using sip_execute_on_image=t38_gateway

Now, one way or another I also want the a-leg to be t38 if possible. Be that via reinvite from FS or sepcifically requested by User. I can't make this work at all.

If FreeSWITCH renegotiates with User and User rejects T38, Freeswitch does not reinvite with the original codecs.

If User requests t38, fax negotiation fails in some cases, although that may be irrelevant.

So, here's my current configuration, that kind of works:

<action application="export" data="fax_enable_t38=true" />
<action application="export" data="sip_execute_on_image=t38_gateway self nocng" />

To test the User end (in this case another FreeSWITCH box for testing):

With T38:

originate {execute_on_answer='t38_gateway peer',fax_verbose=true,ignore_early_media=true,fax_ident=xxxx,fax_header='Test Fax',absolute_codec_string=PCMA,origination_caller_id_number=xxxx}sofia/gateway/xxxx/xxxx &txfax('/home/andrew/test_fax.tiff')

Without T38:

originate {execute_on_answer='t38_gateway peer',fax_verbose=true,ignore_early_media=true,fax_ident=xxxx,fax_header='Test Fax',absolute_codec_string=PCMA,origination_caller_id_number=xxxx}sofia/gateway/xxxx/xxxx &txfax('/home/andrew/test_fax.tiff')

However, the following fails:

originate {fax_enable_t38=true,fax_enable_t38_request=true,fax_verbose=true,ignore_early_media=true,fax_ident=xxxx,fax_header='Test Fax',absolute_codec_string=PCMA,origination_caller_id_number=xxxx}sofia/gateway/xxxx/xxxx &txfax('/home/andrew/test_fax.tiff')

I think this configuration will work for now, the User end can decide freely if they want to send t38 requests to FS or not.

On 4 August 2016 at 14:39, Brian West <brian@freeswitch.org> wrote:
You also do NOT want pass thru set if you're doing this. 

On Thu, Aug 4, 2016 at 4:02 AM, Andrew Cassidy <andrew@cassidywebservices.co.uk> wrote:
Hi all,

Just realised the server I'm having issues with is an old wheezy server running 1.4.26. I will test with latest and report back.

Kind regards,

On 4 August 2016 at 09:55, Andrew Cassidy <andrew@cassidywebservices.co.uk> wrote:
Good morning all,

I've been playing with faxing and t38 over the last few days. I use a wholesale provider who detects and reinvites for t38, and have implemented the same in my systems. Passing t38 through unmodified is not an issue.

The issue I do have, is in the event that the sender refuses the reinvite, I'd like freeswitch to transcode. In theory, this is set up correctly, but see this error message repeated over and over and ultimately the fax fails:

[DEBUG] mod_spandsp_fax.c:1756 sofia/external/xxx@provider.com Error decoding UDPTL (172 bytes)

Every other scenario I have worked through is working fine.

For reference, the fax-specific dialplan entries:

<action application="export" data="fax_enable_t38=true"/>
<action application="export" data="fax_enable_t38_request=true"/>
<action application="export" data="t38_passthru=true"/>
<action application="export" data="nolocal:sip_execute_on_image=t38_gateway self" />
<action application="set" data="execute_on_answer=t38_gateway peer" />

Thanks in advance.

--
Andrew Cassidy BSc (Hons) MBCS SSCA



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